Question

The molar heat capacity of water at constant pressure, $C_{P}$ is 75 $J \, \text{K}^{- 1}mol^{- 1}$ . When 10 kJ of heat is supplied to 1 kg water which is free to expand, the increase in temperature of water is

• A. 2.4 K
• B. 4.8 K
• C. 3.3 K
• D. 7.2 K

Answer 1

Answer: (A)

$\text{q}_{\text{m}} \, \text{=} \, \text{mc} \, \text{ΔT}$
$q_{m}=10\text{ kJ}$ or $10000\text{ J, m}=1000g$
$c=75\text{ J }\text{K}^{- 1}mol^{- 1}$ . Number of moles $=\frac{1000}{18}=55.5 \, mol$
$\text{ΔT} \, \text{=} \, \frac{\text{10000}}{\text{55} \text{.5} \, \times \, \text{75}} \, \text{=} \, \text{2} \text{.4} \, \text{K}$